The present invention relates to aircraft. The invention is more particularly (though not exclusively) concerned with unmanned aerial vehicles (UAVs) and it is in the context of aircraft of this class that the invention will be more particularly described hereinafter. Such vehicles may be used primarily by military forces e.g. for airborne (or in the case of preferred embodiments of the present invention also ground-based) surveillance, reconnaissance, communications relay or the like duties, but may also have civilian applications such as for road traffic monitoring, ground mapping, aerial photography and so forth.